Extending protein functionality: Microfluidization of heat denatured whey protein fibrils

The functional attributes of globular proteins can be extended by controlling the nature of the aggregates they form. In this study, the effect of thermal treatment (85°C/20 min) and high pressure microfluidization (20,000 psi, 1 pass) on the physical properties of whey protein isolate solutions (5-9%; pH 2) was investigated. Heating solutions of native whey protein isolate (8 wt%) under these acidic conditions led to the formation of highly viscous solutions (η = 306 mPa s) with low turbidity (τ = 0.04 cm−1), which was attributed to the formation of protein fibrils (effective d = 310 nm). Microfluidization of these protein fibrils decreased their length (effective d = 97 nm) leading to a substantial reduction in solution viscosity (η = 3.8 mPa s), and a slight reduction in turbidity (τ < 0.03 cm−1). The impact of solution pH (2-7) on the appearance and rheology of native, heated, and heated-microfluidized whey protein isolate solutions was then examined. For all systems, highly turbid solutions (τ > 1 cm−1) were formed at pH values close to the isoelectric point of the whey proteins (pH 4.5) due to protein self-association caused by reduction of the electrostatic repulsion between the protein molecules. Highly viscous or gelled solutions were formed for the heated and heated-microfluidized proteins across a wide pH range, which was attributed to the presence of fibrils. The study showed that the functional attributes of whey proteins can be modulated by thermal and high-pressure homogenization treatment.